This invention relates to a method and an apparatus to compensate for the effect of cross wind on motor vehicle handling.
When driving through a gust of cross wind, vehicles without steering correction are laterally displaced and are turned out of the wind to at least some extent. As a result, the vehicle experiences a steady-state course deviation when it emerges from the cross winds. In addition to the wind force and the direction of the wind relative to the driving direction of the vehicle, the driving speed of the vehicle and its geometry influence the extent of the lateral displacement or change of direction, which therefore differ from one vehicle to the next.
As a rule, the influence of the cross-wind on a vehicle is taken into account during its construction and is kept as low as possible by appropriate design measures. However, for physical reasons, it is not possible to eliminate completely the influence of cross winds on the vehicle handling by passive design measures alone.
It has therefore been attempted to further reduce the influence of cross winds on vehicle handling by the use of sensors to detect cross winds, with either an axle of the vehicle or the steering angle of the wheels of the axle being adjusted in a manner calculated to compensate for the effect of cross winds.
German Patent Document DE-PS 11 08 091 discloses an arrangement which operates in this manner. By way of one pressure measuring point situated respectively on each side of the vehicle, pneumatic pipes lead to chambers on both sides of a diaphragm of a pneumatic control element. The pneumatic control element actuates a hydraulic valve which controls a final control element. In a first embodiment, the final control element with a spring loaded center position displaces the suspension points of an axle of the vehicle relative to the vehicle body; in a second embodiment, it adjusts the steering angle of the wheels of this axle.
However, in this known arrangement, the effect of the pressure difference on the steering angle is predetermined and fixed in advance (largely proportional to the pressure difference), and therefore does not optimize the handling dynamics of the vehicle. Likewise, any disturbance in the approaching air has a direct effect on the steering angle.
According to the German Patent Document DE 23 31 616 A1, influences of cross wind on the vehicle handling are compensated by a steering angle which is proportional to the time derivative of the lateral acceleration of the vehicle. However, for this purpose, the lateral acceleration must be detected by a lateral acceleration sensor, which is relatively expensive, since interfering influences can be removed from its output signal only at a substantial expense. Freedom of such instruments from pulse-type interfering influences in particular is an absolute prerequisite in order to avoid the control system's carrying out uncontrolled pulse-type adjusting movements.
Finally, in German Patent Document DE 38 16 057 C1, an arrangement is disclosed for determining the influences of cross winds on a vehicle. A total of six manometric capsules are arranged on the vehicle, whose pressure values are linked to one another in an expensive manner. Such linking of the pressure values requires relatively high computing expenditures. Since absolute pressure values are required, all sensors must be connected on one side with a reference pressure chamber, which is itself connected with the atmosphere by way of a throttle line, in order to be able to use less expensive differential pressure sensors.
It is an object of the present invention to provide a method and an apparatus for minimizing the influence of cross winds on the handling of a vehicle which requires only relatively low expenditures for sensors to detect the influence of the cross wind, permits essentially free control of a steering element of the vehicle as a function of the quantity or quantities detected by the sensors, and minimizes the influence of the cross wind on the driving dynamics of vehicle.
This object is achieved according to the invention, in which a final control element adjusts an additional steering angle on an axle of the vehicle in such a manner that the yaw angle caused by the transverse force of the wind approaches zero. The additional steering angle is advantageously computed by means of a digital computer; the time response of the computed additional steering angle corresponds to a PDT.sub.1 -response, wherein the differential pressure is the input quantity, and the driving speed is the quantity influencing the transmission parameters.
To detect the influence of the cross wind (that is, the transverse force of the wind on the vehicle), only a single differential pressure sensor is required, which is connected with two pressure measuring points on the vehicle body by way of hoses or lines which, if possible, should have the same length. The pressure measuring points are situated symmetrically with respect to the vertically extending longitudinal plane of the vehicle, on its forward portion, for example, on the front fenders. They are placed in an area of the outer skin of the vehicle body which is free of turbulences and from which, even under unfavorable approach flow conditions, the flow does not separate.
The reaction of the final control element to cross wind is determined as a function of the vehicle's entering into or emerging from a cross wind gust, by means of different parameter sets. Driving into/out of the gust of cross wind is detected by filtering measured values of the differential pressure by means of a low-pass filter, and determining a rise or fall of the differential pressure from the differences between successive measured values of the filtered differential pressure.
The principal advantages of the invention are that it requires only relatively low expenditures for sensors to detect the influence of the cross wind; it permits essentially free control of the steering element of the vehicle as a function of the quantity or quantities detected by the sensors; and it is distinguished by the fact that optimal countermeasures are taken against the influence of the cross wind on the driving dynamics of the vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.